Flue Gas Desulfurization sludge (FGD, CaSO4·2H2O, CaSO3·1/2H2O) is a waste by-product produced when sorbent slurry is passed through wet scrubbers. FGD contains higher concentrations of Ca, S, Si, Fe, Al and Br making it of great environmental concern. Presently only 16% of 24 million metric tons (MT) of FGD sludge produced is being recycled; the rest is disposed in landfills. This research was focused towards stabilizing FGD sludge with Portland Type II cement and Class C fly ash to produce lightweight fill material to be used in the construction of coastal devices. The specific objectives included the development of a FGD briquette composition that under submerged conditions: 1) maintained physical integrity, 2) has minimal dissolution of Ca2+ and SO42- to the surroundings 3) demonstrates acceptable engineering properties of a fill material and 4) economical to fabricate.

The leaching behavior of all the FGD composites was found to be similar and the effective diffusion coefficients from the 77-day dynamic leaching test ranged 4.87–7.01 x 10-13 m2·s-1and 0.67– 3.71 x 10-13 m2·s-1, for calcium and sulfate respectively. The metal concentrations in the TCLP leachate were well below the USEPA toxicity characteristics limits. The engineering properties test results indicated that the composite material could be classified as well-graded gravel or well-graded sand with little or no fines. The USCS classification would also qualify FGD briquettes as a potential fill material in embankment construction having excellent workability and shear angle of 48° to 49°. For all the tests conducted the 63%:35%:2% briquette fabricated in small size performed better than the large size briquette.